Cavalier of Night, Glasspool Mimic // Glasspool Shore, and Grimgrin, Corpse-Born

Prerequisites

• Cavalier of Night on the battlefield
• Glasspool Mimic // Glasspool Shore on the battlefield
• Grimgrin, Corpse-Born on the battlefield

Steps

1. Activate Grimgrin by sacrificing Glasspool Mimic
2. When Glasspool Mimic dies, its last ability from Cavalier of Night triggers, returning itself from your graveyard to the battlefield as a copy of Cavalier of Night
3. When Glasspool Mimic enters the battlefield, its first triggered ability from Cavalier of Night triggers; choose not to sacrifice a creature
4. Resolve the Grimgrin ability from step 1
5. Repeat

Results

• Infinite +1/+1 counters on a creature
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers